Kepler-1861 b
Astrophysical Synthesis & Habitability Characterization
Kepler-1861 b is a confirmed sub-neptune exoplanet orbiting the star Kepler-1861, located approximately 2707 light-years (829.99 parsecs) from the Solar System. First announced in 2021 by Kepler using the Transit detection technique (producing an estimated primary transit depth of 0.0217% across the stellar disk), this world measures 2.207 Earth radii and has a measured mass of 5.5 Earth masses. Combining its mass and radius yields a mean bulk density of 2.82 g/cm³ (an intermediate density indicative of a deep water-ice mantle or dense volatile envelope), a surface gravity of 1.13 g⊕ (11.08 m/s²), and an escape velocity of 17.7 km/s.
In its orbital architecture around Kepler-1861, Kepler-1861 b completes one full revolution every 40.031 Earth days at a semi-major axis of 0.24082 AU (orbiting interior to Mercury's 0.387 AU benchmark in the Solar System). Its mean orbital velocity is approximately 65.4 km/s (compared to Earth's 29.8 km/s). The orbit is modeled as circular (e = 0.00), maintaining a constant stellar distance throughout its year.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 617 K (+344°C / +651°F) and receiving 31.50 S⊕ (~42,872 W/m²), Kepler-1861 b orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star Kepler-1861 is classified as a stellar host with an effective photospheric temperature of 5,855 K, a radius of 1.373 R☉, a mass of 1.161 M☉, an estimated bolometric luminosity of 1.988 L☉. Stellar evolution modeling indicates an estimated stellar age of 4.57 Gyr and a metallicity of [Fe/H] = 0.26 dex (metal-rich relative to the Sun). From Earth, Kepler-1861 shines at apparent V-band magnitude 13.709 (faint and requiring research-grade or CCD telescopic photometry) in the Northern celestial hemisphere.
Methodology: Computed using the Schulze-Makuch et al. (2011) weighted metric comparing physical interior (radius, estimated density) and surface thermal regime (escape velocity, equilibrium temperature).
Discovery Facility: Kepler · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | Kepler-1861 |
| Spectral Type | Unclassified |
| Effective Temp (Teff) | 5,855 K |
| Stellar Radius | 1.3730 R☉ |
| Stellar Mass | 1.1610 M☉ |
| Bolometric Luminosity | 1.988 L☉ |
| Metallicity [Fe/H] | 0.260 dex |
| Stellar Age | 4.570 Gyr |
| Apparent Magnitude | V: 13.709 · G: 13.652 |
| System Architecture | 1 Star, 1 Planet |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.240820 AU |
| Orbital Period | 40.031 days |
| Mean Orbital Velocity | 65.4 km/s |
| Orbital Eccentricity (e) | 0.00000 |
| Orbital Inclination (i) | 89.7000° |
| Mean Bulk Density | 2.82 g/cm³ (17.7 km/s vesc) |
| Insolation Flux | 31.5000 S⊕ (~42,872 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 2707.000 LY (829.985 pc) |